Hydroquinone sulphonates are used in some types of photographic developer solutions. Hydroquinone monosulphonate salts are generally produced industrially by processes such as fusing benzoquinone with potassium sulphate which yield a product containing considerable quantities of impurities and which is considerably more expensive than hydroquinone itself.
Hydroquinone monosulphonate is known to be produced when a photographic developer containing hydroquinone, a salt of sulphurous acid and a developing agent such as Metol (4-methylaminophenol) is used to develop an exposed photographic film. Hydroquinone monosulphonate may replace hydroquinone in certain specialized developing solutions. In these developing solutions, a number of advantages may be gained by using hydroquinone monosulphonate, particularly when it is used in the first or black or white developer of a reversal process for the production of a colour slide. Hydroquinone monosulphonate may be used in the E6 process developed by the Kodak company and this E6 process has now been adopted by major film manufacturers including Kodak, Fuji Photofilm Company Limited and the 3M Company. The wider use of hydroquinone monosulphonate in developer solutions is hampered by its present excessive cost.
Both potassium and sodium hydroquinone monosulphonate are expensive to use, not only because of their basic cost but because a larger weight of the chemical has to be used than would be required if hydroquinone was present in the developer rather than the hydroquinone monosulphonate. Also potassium or sodium hydroquinone monosulphates are not readily available, so manufacturers of kits and suppliers of solutions to the commercial film developing companies tend to use less satisfactory alternatives.
Recovery of sodium or potassium hydroquinone monosulphonate from solution is difficult and expensive, primarily as a result of its high solubility, so purification of the normal commercial product is difficult when a solid product is desired.